Refining plasticizer



p 1936 M. J. REID 2,053,532

REFINING PLASTICIZER Filed Sept. 1 1, 1934 2 Sheets$heet l Sept. 8, 1936. M. J. REID' 2 REFINING PLASTICIZER Filed Sept. 11, 1954 2 Sheets-Sheet 2 mvinlRei Patented Sept. 1936 warren STATES PATENT OFFICE Marvin 3. Reid, Rochester, N. Y assignor to Eastman Kodak Company, Wheat er, N. Y., a --corporation or New York Application September 11, 1934, Serial No. 743,611

. claims. (oi. zoo-99.20)

contaminated with various solid impurities such as metallic salts and nitrocellulose and the like.

As is well known, photographic film and other cellulose derivative plastic materials usually contain various valuable ingredients which experience has shown may bevery profitably recovered.

In the case of photographic film the most important of these are silver or silver salts contained in the gelatino-silver halide emulsion layer, the

plasticizers employed in the support, and the material of the support itself. The present invention is concerned primarily with recovery of the plasticizing material in a substantially 100% pure form.

Triphenyl phosphate may be taken as illustrative of the plasticizing materials which are amenable to recovery according to the present invention. In my 'copending application, Serial No. 612,850, filed May 29, 1932, there is described a process for the recovery of various plasticizers from film scrap by leaching with methyl alcohol, followed by precipitation of the dissolved nitrocellulose and triphenyl phosphate by the addition of water to the leaching solution, the triphenyl phosphate being obtained at that stage of the process in a relatively wet and impure form containing relatively large amounts of nitrocellulose.

In that application I have also described a method whereby the plasticizer may be obtained in a pure form by dissolving the crude plasticizer in a hydrocarbon solvent therefor followed by crystallization. The present process constitutes an alternative and improved method for refining the crude plasticizer in pure form and in a condition in which it may be immediately reused in the preparation of cellulose ester solutions or dopes for making photographic films or other products. The instant process is a marked improvement over the method of refining the crude plasticizer by the use of hydrocarbon solvents just referred to as will be apparent from the following description.

In order to refine a plasticizer such as triphenyl phosphate by the method just alluded to, it is necessary to dissolve the plasticizer in the hydro- 50 carbon. The material in the crude form in which it exists after the precipitation step almost always contains an appreciable amount of nitrocellulose and solid impurities such as iron salts and other materials which are unavoidably picked up during 55 the processes of manufacturing the original plastic product from which it is obtained. These impurities are in most cases insoluble and are held in suspension in the solution. It is accordingly necessary to remove them mechanically, either by filtration or centrifuging. It is, of course, nec- 5 essary to maintain the hydrocarbon solvent at a relatively high temperature during all of these operations in order that the dissolved plasticizer may be brought into and held in solution. After the suspended impurities are mechanically re- 1 moved as just stated, the temperature oi. the solution is lowered, the plasticizer crystallizes out and is separated from the hydrocarbon solvent by filtration or other mechanical means. It will thus be seen that this method of refining involves a 1 large out-lay for the various pieces of apparatus necessary to handle the plasticizer solution, separate the impurities and maintain the solution at the proper temperature; Not only is such a method likely to be costly from the standpoint 20 of equipment, but the losses through evaporation of the volatile solvents are relatively very great. In addition to these disadvantages, which are inherent in such a method, there is constant danger of fire or explosion due to the highly 25 inflammable nature of the liquids involved in the operation.

It is the principal object of the present invention to obviate the difiiculties outlined above and to provide a process in which a crude plasticizer, 30

especially one containing such impurities as nitrocellulose, water, metallic salts and the like, may

be easily obtained in substantially 100% pure condition. A further object of the invention is to provide a method of refining a crude plasticizer 35 whereby the plasticizer is obtained in a form in which it may be immediately re-used in the manufacture of cellulosederivative plastics. A specific object of the invention is to provide a method of refining impure triphenyl phosphate without 40 the employment of hydrocarbon solvents. A still more specific obiectof the invention is to obtain from an impure form of triphenyl phosphate 9. solution thereof in ethylene chloride, which solution is in sufiiciently pure form to enable it to be used directly in the manufacture of a cellulose derivative dope. Other objects will appear hereinafter. 1

These objects are accomplished by the following invention which, in its broadest aspects, comprises dissolving the crude plasticizer in ethylene chloride and passing the resulting solution through a super-centrifuge, obtaining as the product of such treatment a clear water-white solution of the plasticizer in ethylene chloride.

In the following dmcription and example, which are included merely for purposes of illustration and not as a limitation of my invention, I have setforth several of the preferred embodiments thereof.

The invention may be conveniently illustrated by reference to the. refining of a crude form of triphenyl phosphate such as would be obtained at one stage of the process described in my application, Serial No. 612,850, above referred to, and containing as'impurities varying percentages of water, nitrocellulose, iron-rust, and other solid materials. This crude plasticizer is dissolved in ethylene chloride in the ratio of one part by s the solution and the various materials contained in the mixture will separate on standing into various layers according to their respective specific gravities. The ethylene chloride with a specific gravity of 1.25 forms the bottom layer, the water (specific gravity =1.0) forms the top layer and the nitrocellulose (specific gravity: 1-1.2) constituting an intermediate layer between the ethylene chloride and the water; Most of the solidmaterials are also suspended in the water layer. This solution is then passed through a super-centrifuge provided with a separating type bowl in a manner which will now be described in detail.

In the accompanying drawings in which like numerals refer to like parts: 7 A

Fig. l is a schematic elevational view of one type of apparatus suitable. for carrying out the process of the invention.

Fig. 2 is a partial, vertical sectional elevation through the super-centrifuge shown in Fig. 1 illustrating the internal structure of the device, the upper portion of the enclosing casing being broken away and the driving mechanism omitted.

Fig. 3 is a perspective view of the 3-wing forming a part of the internal mechanism of the centrifuge bowl.

Fig. 4 is a horizontal, sectional view on the line 44 of Fig. 2 showing the 3-wing in place within the centrifuge chamber.

Fig. 5 is a. horizontal section taken along the line 5-5 of Fig. 2 illustrating the commingling of the liquid layers in the lower part of the centrifuge.

Fig. 6 is also a horizontal section taken along the line 5'5 of Fig. 2 illustrating the separation of the various liquid layers in the centrifuge at the upper part of the device.

Referring to Fig. 1, the numeral l designates a mixing tank for the ethylene chloride solution of crude plasticizer to be treated; This tank is provided with an agitating device l| driven by means of pulley I! from a source of power (not shown). Tank M, which is conveniently supported upon platform l3 at a height suflicient to maintain at least a -ft. head on the feed to the super-centrifuge, is provided with an outlet conduit l4 controlled by valve l5.

Conduit I4 is connected to the upper half of a screen pot l6 fitted with a inch mesh brass screen I! through which the solution conducted from tank I. must pass on its way to the centrifuge. The screen pot is provided with a feed pipe l8 of relatively small diameter which conveys the filtered solution to the inlet IQ of the centrifuge 20.

The centrifuge 2|! is or the super-centrifuge type and includes a bowl appropriately attached to shaft 2| driven by pulley 22 from a source of power (not shown) at a speed of approximately 14,000 R. P. M. The centrifuge is provided with heavy liquid outlet 23 which is connected to storage tank 24 thro h trapped conduit 25. Likewise, light liquid outlet 26 is connected through trapped conduit 21 to a small feed tank 28. Both conduits 25 and 21 are provided with sight glasses Hand 30, respectively.

Feed tank 28 is provided with suction pipe ll connected to pump 32 which in turn is connected by conduit to the top ofthe mixing tank l0. Feed tank 28 is vented back to the dome 34 of the centrifuge 20 by means of conduit 35. The centrifuge is also connected to the feed tank 28 by means of drain conduit 36, which conduit takes care of any spills due to a plugged centrifuge nozzle or to drainage from the bowl when the centrifuge is shut down.

The tank 24 is also provided with a suitable vent pipe 31 and with suction pipe 38 for removing the solution contained therein as desired.

Referring to Fig. 2, the numeral 39 designates the casing of one type of super-centrifuge which is suitable for the carrying out of the herein described process. The device illustrated is one which is completely enclosed in a casing and may be considered substantially pressure tight. The casing 39 encloses chamber 40 within which the cylindrical centrifuge bowl 4| is centrally disposed.

Bowl 4| is connected to drive shaft 42 through cap 43 threaded and welded to bowl 4|. Cap 43, carries adjustable ring-dam 44. The cap 43 also is provided with darn 46 and with ports 41 and 40 through which the heavy and light liquids, respectively, pass from the bowl 4|. Light liquid passes through port 48, impinges'upon the wall of the casing 49, and thence descends through conduit 50 to outlet 26. In like manner heavy liquid pass ing from port 41 impinges upon partition 5| and thence passes downwardly into conduit 52 to outlet 23.

The lower end of the bowl 4| is closed by member 53 threaded thereto. Member 53 includes tubular projection 54 which extends downwardly over the inlet nozzle or jet 55 which is threaded to the inner end of feed pipe l8 leading from the screen pot to the centrifuge, as previously described. The nozzle 55 is surrounded by guide member 56 which carries suitable bearing mechanism 51 in which the tubular member 54 is adapted to rotate.

Referring to Figs. 3 and 4, the numeral 59 designates a 3-wing whichis adapted to be inserted within the centrifuge bowl 4| in such manner as to provide for all of the liquid in its vicinity rotating with the bowl as the bowl turns.

In carrying out the process of my invention, the tank I0 is filled about two-thirds full of pure ethylene chloride. Crude triphenyl phosphate, such as that produced at one stage of the process described in my co-pending application 612,850 above referred and containing a relatively large amount of water, nitrocellulose metallic and other solid impurities of various kinds, is then added in an amount suflicient to make up an approximately solution of triphenyl phosphate in ethylene chloride. It is rather important to add the crude triphenyl phosphate to the solvent, since the nitrocellulose impurities are appreciably soluble in a concentrated solution of triphenyl phosphate in ethylene chloride. However, for the purposes of my invention, a solution aoaassa.

containing less than 15% triphenyl phosphate will not dissolve suillcient nitrocellulose to be troublesome. After agitating a few minutes to dissolve the triphenyl phosphate, the batch is ready for further treatment as follows, all of the various operations being carried out at room temperature.

In order to start the super-centrifuge operating with no water or impurities discharging with the triphenyl phosphate-ethylene chloride solution, it is necessary first to prime the machine by feeding pure ethylene chloride to the centrifuge until it discharges through the outlet 23. This amount of ethylene chloride is suflicient to fill the space which the heavy layers later occupy in the bowl. After this is done, any amount of a lighter immiscible liquid can be added without any of it discharging with the heavy liquid.

Following the priming operation just described, valve I5 is opened and the impure solution of triphenyl phosphate is let into screen pot I6 where of the bowl 4! where it strikes the 3-post assembly 60 which, in conjunction with the super-centrifugal force, throws it outwardly to the wall of the bowl which is revolving at the rate of about 14,000 R. P. M.

Due to the super-centrifugal force exerted upon the liquid mixture, it immediately begins to separate into layers according to the specific gravity of its various component parts. The section of Fig. 5 shows the layers as they have separated in the lower end of the centrifuge how! after the machine has run for some little time. The solid black ring D next to the wall of the bowl is the accumulation of dirt, grit, rust, and other solid material, all of which has a higher specific gravity than the water and triphenyl phosphate-ethylene chloride solution, represented by the dotted intermediate ring S. The inner ring W represents the water layer which carries with it the undissolved nitrocellulose while A represents the air space existing at the center of the whirling body of liquid. At this point the layers are not completely separated and are represented as being somewhat intermingled.

As the mixture is fed into the bowl it rises and is eventually discharged at the top. After rising about six inches from the bottom of the bowl, it is picked up by the 3-wing 59 and from that point on the liquid must rotate with the bowl, thus being subjected to the full centrifugal force available. By-the time the mixture reaches the point indicated bythe line 6-6 of Fig. 2, the layers S and W are sharply defined. It is very seldom. that enoughdirt or other solid impurities collect to allow the dirt layer ever to reach this point. The nitrocellulose is at this point separated in an extremely thin layer between the water layer and the ethylene chloride solution layer, it having a specific gravity between that of water and the solution.

When the mixture reaches the dam 46 at the top of the bowl, it is separated into two fractions. The heavier or triphenyl phosphate-ethylene chloride fraction flows over the outer edge of the dam up over the adjustable ring dam 44, through the ports 41 and then into the conduit 52 and out through the outlet 23. ring dam fixes the height of the outer or heavier layer in the bowl and varies according to the The adjustment of the.

specific gravities and is best determined by trial and error methods. 1

The lighter water layer flows over the inner edge of the dam 46 and out through the ports 40 which spill into the upper cover 49 and thence into conduit 50 and outlet 20. .When sufficient nitrocellulose accumulates between the two liquid layers, it is washed over the inner edge of dam 46 with the water and discharged therewith back into tank 28.

It is to be noted that the discharge from the inner layer or port 48 of the bowl is returned to the tank 28 and thence by means of pump 32 to the mixing tank again. This procedure gives the maximum yield of triphenyl phosphate-ethylene chloride solution, because in the early stages of the run and in the priming, the volume of ethylene chloride is so much greater than the volume of water that some of the heavier layer discharges with the lighter. By returning the water layer to the mixing tank, there can be no appreciable loss of solvent.

The above outlined process is continued until no more triphenyl phosphate-ethylene chloride solution is discharged from the port 23 of the centrifuge. This signifies that only water and impurities remain to be circulated. The discharge through the outlet 26 is then diverted to waste pipe 63 by closing valve 6! and opening valve 52, after which the mixing tank is made ready for another batch. It will, of course, be necessary to empty the screen pot periodically, the frequency depending upon the nature of the crude material being dissolved.

The liquid which passes from the centrifuge into the tank 24 through the outlet 23 is a waterwhite solution of triphenyl phosphate in ethylene chloride, and this may be used directly for the manufacture of dopes for the manufacture of photographic film support. In other words, the solution is of such purity and clarity'that it may be used directly for all dopes in which ethylene chloride is employed as a solvent. 0n the other hand, if it is desired to obtain the triphenyl phosphate in solid form, it can be crystallized from solution according to the usual crystallization procedure known to those skilled in the art.

' While I have found it convenient to describe my invention by reference to the so-called Sharples type of supercentrifuge having a long narrow bowl adapted to rotate at the relatively high speed of 14,000 revolutions per minute, other types of centrifuge may be employed with equally satisfactory results, so long as they are capable of developing the required centrifugal force. For example, instead of the narrow bowl, high speed machine, I may employ the so-called De Laval type of supercentrifuge employing a comparativewhere F is centrifugal force, R is the radius of the revolving bowl in feet; W is weight of material upon which centrifugal force is being applied; and N is the number of revolutions per minute. For any given material W is a constant. Likewise for any given machine, R is a constant. Therefore, in a given machine, the centrifugal force may be varied by varying'the speed. of the machine, this terial contaminated by corrosion of equipment or storage vessels, the centrifuged solution is sumciently colored to make its use objectionable, particularly in the manufacture of photographic film support. This diiliculty may, however, be easily overcome by adding a small percentage, say about .05%, of activated carbon to the solution,

mixing well, and filtering. The solution obtained by this treatment is water-white in clarity.

It will be seen from the above description that in the centrifuging operation 4 distinct layers are formed: (1) the layer of heavy dirt, grit, sand, or rust, and other solid materials which accumulate at the lower portion of the centrifuge bowl having a specific gravity considerably in excess of 1.2 (2) the triphenyl phosphate-ethylene chloride solution, having a specific gravity of about 1.25, (3) the insoluble nitrocellulose impurities, having a specific gravity between 1.25 and 1.0, and (4) the water layer, having a specific gravity of 1.0.

' It will be noted that all of the impurities originally present in the crude plasticizer are with the possible exception of small amounts of iron salts,

or dyes, substantially insoluble in the ethylene chloride, thus making it possible to effectively remove them by the action of the super-centrifuge.

It will be evident that my process has certain outstanding advantages, one of the most important of which is the small investment for appaof low solvent losses, these representing only approximately 2% as compared to or over when using hydrocarbon solvents and crystallizing the plasticizer from such solutions. 7

Aside from these advantages, probably the outstanding feature of my process is the fact, as mentioned above, that I am enabled to obtain the plasticizer inthe form of a solution which. may be employed directly in the production of cellulose derivative solutions or dopesfor the manufacture of films, sheeting and the like. It is quite unnecessary for example, to crystallize the triphenyl phosphate from the ethylene chloride solution, since as is well known, ethylene chloride, as well as triphenyl phosphate, are ingredients commonly employed in the preparation of cellulose acetate and other cellulose organic ester dopes derivative dopes. One of the features of the present invention is that it eliminates this crystallizing step by obtaining the plasticizer in the form of a solution which is immediately reusable and compatible with the various cellulose esters.

As many apparently widely different embodiments of this invention may be made without departing from'the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims;

What I claim as new and desire to be secured by Letters Patent of the United States is:

1. The process of refining impure triphenyl phosphate which comprises dissolving the triphenyl phosphate in a solvent in which the impurities are insoluble and separating the impurities therefrom by subjecting the solution to the inprises dissolving the crude triphenyl phosphatein an organic solvent in which the impurities are insoluble and subjecting the resulting solution to the influence of the centrifugal force obtained by passing the solution through the rotating bowl of a supercentrifugal operating at such a speed as to exert a centrifugal force equivalent to about thirteen thousand times the force of gravity, whereby a clear solution of triphenyl phosphate in the solvent is obtained.

4. The process of refining crude triphenyl phosphate containing as impurities nitrocellulose, water and inorganic compounds, which comprises dissolving the triphenyl phosphate in ethylene dichloride and subjecting the resulting solution to the influence of the centrifugal force of approximately thirteen thousand times the force of gravity obtained by passing the solutionthrough the rapidly rotating bowl of a supercentrifuge.

5. The process of refining crude triphenyl phosphate containing as impurities nitrocellulose, water and inorganic compounds, which 'comprises dissolving the triphenyl phosphate in ethylene chloride in the ratio of one part by weight of triphenyl phosphate to about 10 to 30 parts by weightof ethylene dichloride and subjecting the resulting solution to the influence of the centrifugal force obtained by passing the solution through the bowl of a supercentrifuge'rotating'at a speed to obtain'a force of approximately thirteen thousand times the force of gravity, whereby a pure substantially water-white solution of triphenyl phosphate in ethylene chloride suitable for film manufacture is obtained.

MARVIN J. REID. 

